Glass cleaners are often available in a form that is ready to use. A consumer will purchase a glass cleaner, such as, a window cleaner, and use the glass cleaner directly on a glass surface. Alternatively, the glass cleaner may be provided as a concentrate solution which is diluted with dilution water to form a use solution at the point of use or at an intermediate location. Diluting the concentrate at the point of use or at an intermediate location reduces the cost and the space required to transport and store the concentrate solution.
One reason that glass cleaners are provided in a form that is ready to use is to control the presence of “hardness” in the water used to prepare the ready to use glass cleaner, which has a tendency to cause precipitation of some components of the solution, such as anionic surfactants. Water hardness may also lead to aesthetically unpleasant streaking on glass surfaces.
Hardness is defined as the concentration of multivalent cations. Typically multivalent cations include Ca2+ and Mg2+ ions. Iron, aluminum and manganese can also contribute to hardness. One measurement of hardness defines hardness in terms of the calcium carbonate concentration where 1 grain is equivalent to 17.1 mg of calcium carbonate per liter.
Glass cleaners also typically include a volatile organic compound (VOC) such as but not limited to solvents such as ethanol and alkanol amines such as monoethanolamine. A compound is non-volatile if its vapor pressure is below 0.1 mm Hg at 20° C. VOCs have been the subject of regulation by different government entities, the most prominent regulations having been established by the California Air Resource Board in its General Consumer Products Regulation. Thus, it may be desirable to formulate glass cleaners containing low or no VOCs.